Use the solar energy with a solar thermal system

With a solar thermal system, you can harness the sun's free energy to reduce your monthly energy costs. In addition, by installing a solar thermal system, you are signaling your responsibility to the environment by sustainably reducing CO₂ emissions. By investing in such a system, you also increase the value of your property at the same time. With Viessmann technology, you are relying on future security and the optimum interaction of all system components. With more than 40 years of experience in the development and manufacture of solar thermal systems, you can rely on our technical expertise and top quality. Solar thermal is an excellent addition to a heating system.

Regardless of whether you decide on a new condensing heating system using oil or gas, a heating system for wood or even a heat pump - all Viessmann systems are designed for combination with a solar thermal system.


> Thermische Solaranlagen (PDF, 945 KB)

Flat plate and tube collectors


What is a solar thermal system?

In principle, a solar thermal system is a solar system that can be used for water heating and heating support. Due to the free available solar energy you do not only save fossil energy. The investment in a solar thermal system pays for itself within a few years. This is because there are no costs for an energy source.

In order to use the sun's energy, collectors are required that capture this radiation. Viessmann Vitosol tubular and flat-plate collectors have been developed for this purpose. They absorb the sun's rays and convert them into usable heat.

In addition to the collectors, a solar thermal system consists of an absorber, a solar circuit and a solar fluid or solar medium. When the rays hit the collectors, this energy is converted into heat in the absorber. It is first conveyed to the buffer tank or drinking water storage tank and from there distributed through the circuit in the household - either as a support for the heating circuit or for heating the domestic water. The heat is first transported to the corresponding storage tank by means of a medium - the solar fluid. From the drinking water storage tank, the heat then reaches the taps such as the faucet or shower in the form of the hot water as required.

Differentiation according to application

In principle, you have the option of using solar energy to heat drinking water and support heating. The savings in oil or gas are considerable in any case: with a solar system, you use a good 60 percent less energy per year that would otherwise be needed to heat water for your daily needs. If you combine the heating of drinking water and heating water, the annual savings are around 35 percent of the total energy required.

Solar thermal energy for domestic hot water

The heart of this solution is the bivalent DHW cylinder, such as the Vitocell 300-B. When there is sufficient solar radiation, the solar medium in the solar thermal system heats the water in the DHW cylinder via the lower heat exchanger.

If the temperature drops due to water withdrawal, for example when taking a bath or shower, the boiler switches on as required for additional heating via the second circuit.

The Vitocell product range is a good complement to solar thermal, allowing hot water to be heated with solar and then stored temporarily. This ensures a high level of convenience. You are welcome to use the bivalent DHW cylinders Vitocell 100-U/W or Vitocell 100-W, combi cylinders as well as heating water buffer cylinders such as Vitocell 360-M. We offer the right DHW cylinder for every need. All of them can be easily connected to solar thermal.

Solar system with bivalent hot water tank

But what should you consider in advance in the design?

As a rule of thumb for the design in a one- or two-family house, if the collector area is oriented between southeast and southwest, 1.5 m² flat-plate collector or 1.0 m² tube collector area can be assumed per 100 liter storage volume. To compensate for reduced yields caused by unfavorable orientation or inclination, the collector area can be increased somewhat.

Solar thermal energy for domestic hot water and central heating backup

The solar medium heated in the solar collectors can be used not only for domestic hot water heating but also for additional heating of the heating water.

For this purpose, the heating circuit uses the water in the solar storage tank, which is continuously heated by the solar collectors, via a heat exchanger. The control system checks whether the desired room temperature can be reached. If the temperature is below the setpoint, the boiler also switches on.

Solar system for domestic hot water and heating support

Can you also combine solar thermal with conventional radiators?

A common misconception is that solar thermal for heating support is only possible with underfloor heating systems. Classic radiators can also be used. The yields are only insignificantly lower on an annual average and are determined primarily by the somewhat higher return temperatures from the radiators.

How does a solar system work?

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How does solar thermal work?
Our expert Carsten Kuhlmann explains how a solar thermal system works.